Báo cáo hóa học: " Assembly of Silver Nanoparticles into Hollow Spheres Using Eu(III) Compound based on Trifluorothenoyl-Acetone" doc

NANO EXPRESS
Assembly of Silver Nanoparticles into Hollow Spheres Using
Eu(III) Compound based on Trifluorothenoyl-Acetone
Youyi Sun Æ Yaqing Liu Æ Guizhe Zhao Æ
Qijin Zhang
Received: 25 October 2007 / Accepted: 9 January 2008 / Published online: 26 February 2008
Ó to the authors 2008
Abstract The preparation of luminescent silver hollow
spheres using Eu(III) compound based on trifluorothenoyl-
acetone is described. The structure and size of silver hollow
spheres were determined by TEM images. The result shows
the formation of hollow structure and average size of the
silver hollow spheres (0.9 lm). The silver hollow spheres
were further characterized by UV absorption spectrum,
SNOM and SEM images, suggesting them to be formed by
self-assemble of some isolated silver nanoparticles. The
luminescent properties of them were also investigated and
they are shown to be high emission strength; moreover, they
offer the distinct advantage of a lower packing density
compared with other commercial luminescent products.
Keywords Assemble Á Silver nanoparticles Á Hollow Á
Luminescence
Introduction
Inorganic hollow spheres of nanometer to micrometer
dimensions represent an important class of materials, and
are attended for wide potential applications [1], such as
catalysts, fillers, coatings, and lightweight structural mate-
rials owing to their low density, large specific area, and
surface permeability [2–5]. Especially, noble metal hollow
spheres have attracted lots of attention for their remarkable
optical properties [6, 7]. However, there are few works to

report preparation of noble metal hollow spheres. Only,
previous efforts to prepare noble metal hollow spheres have
been focused on polymer-surfactant compels micelles [8]
and using template methods [9]. The nanometer silver
hollow spheres are difficult to be obtained and should be
removed of the core, resulting in breaking of shell by these
methods. Moreover, the functional metal hollow spheres
cannot be obtained. In the design of multicompositional
materials with spatially defined arrangements of the dif-
ferent components, block copolypeptides may be highly
useful as structure-directing agents for nanoparticle
assembly [10]. It is well-known that noble metals like gold
and silver are capable of existing in the unoxidized state at
the nanoscale and offer a unique surface chemistry that
allows them to be used as platforms for self-assembly layers
of organic molecules [11–14]. So, it is expected to prepare
the nanometer noble metal hollow spheres by crystal self-
assemble method under functional organic molecules
assistant, which is easy to prepare and control. Furthermore,
the hollow spheres containing functional molecules are
expected to be functional properties.
So, here, a new route of synthesis silver hollow spheres
is developed. The silver hollow spheres are formed by the
self-assemble of silver nanoparticles assisted functional
molecules of Eu(TTA)
3
Á 2H
2
O. The Eu(III) organome-
tallic compounds of Eu(TTA)

3
Á 2H
2
O as the dispersion
and bridge of silver nanoparticle results in the self-
assemble of them, along a certain axis in the xy-plane and
the curl and extension of Eu(III) organometallic in a mixed
Y. Sun (&) Á Y. Liu Á G. Zhao
College of Materials Science and Engineering, North University
of China, Taiyuan, Shangxi 030051, P.R. China
e-mail:
Y. Sun Á Y. Liu Á G. Zhao
Research Center for Engineering Technology of Polymeric
Composites of Shangxi, North University of China, Taiyuan,
Shangxi 030051, P.R. China
Y. Sun Á Q. Zhang
Department of Polymer Science and Engineering, University
of Science and Technology of China, Hefei, Anhui 230026,
P.R. China
123
Nanoscale Res Lett (2008) 3:82–86
DOI 10.1007/s11671-008-9118-4
solvent microenvironments for confining the 3D growth of
silver hollow spheres. In other way, the fluorescence of
silver hollow spheres is further observed, which is expected
to apply in optical materials.
Experiment Sections
Synthesis of Rare-earth Complexes
Eu(TTA)
3

Á 2H
2
O (HTTA: trifluorothenoyl-acetone) were
synthesized according to the literature [15] and the struc-
ture is shown in Scheme 1 and is confirmed by IR analysis,
such as the C=O group at 1,614.5 cm
-1
,CF
3
group at
1,357.4 cm
-1
, C=C group at 1,541.8 cm
-1
, and the Eu–O
at 638.9 and 579.8 cm
-1
. The result is consistent with
previous work [15].
Preparation of Silver Hollow Spheres
Silver hollow spheres were prepared according to the
process as shown in Scheme 1. The first step is to syn-
thesize the Ag colloidal solution in the presence of
Eu(TTA)
3
Á 2H
2
O complex according to the literature [16].
The morphology and size of silver nanoparticles and the
surface plasma on resonant absorption peak are determined

to be sphere with an average size of 21.5 and 425.2 nm by
transmission electron microscope (TEM) and UV–Vis
absorption spectrum, respectively. In the second step, the
silver colloidal TFH solution with a concentration of
6.34 9 10
-4
M was obtain and added to be 1 mmol free
Eu(TTA)
3
Á 2H
2
O complex. After this, centrifuging
(3,000 rpm) gave a brown acetone/water precipitate, and
supernatant solution containing excess Eu(TTA)
3
Á 2H
2
O
was extracted. The precipitates were again dissolved to
acetone. The purification procedure was repeated for three
times. Morphology and size of the sample was obtained by
using TEM, scanning electron microscopy (SEM), and
scanning near-field optical microscopy (SNOM). The
samples were also characterized by UV–Vis spectroscopy
and fluorescence spectroscopy.
Results and Discussions
The silver/Eu(TTA)
3
Á 2H
2

O composite nanoparticles were
prepared by the interaction between Ag nanoparticles and
thiophene chromophores group of Eu(TTA)
3
Á 2H
2
O, and
the CF
3
groups of Eu(TTA)
3
Á 2H
2
O extend away from the
Ag nanoparticle to provide solubility of the nanoparticles,
which has been discussed in previous work [16]. So it is
not discussed in detail here. It is further found that if
the concentration of silver/Eu(TTA)
3
Á 2H
2
O composite
nanoparticles is kept at more than 6.34 9 10
-4
M and
1 mmol free Eu(TTA)
3
Á 2H
2
O is present in the solution,

silver hollow spheres are formed by self-assemble of silver/
Eu(TTA)
3
Á 2H
2
O composite nanoparticles as shown in
Scheme 1. Free Eu(TTA)
3
Á 2H
2
O is as bridge of silver/
Eu(TTA)
3
Á 2H
2
O composite nanoparticles by the interac-
tion between Ag nanoparticles and thiophene chromophores,
too.
The formation of silver hollow spheres is determined
by the TEM images as shown in Fig. 1. These spherical
particles as shown in Fig. 1a have pale regions in the
central parts in contrast to darks, indicating them to be
hollow structure. Figure 1a further shows the size range
from 0.6 to 1.5 lm and the average size is 0.9 lm.
Compared with the silver hollow spheres previously
Scheme 1 Illustration of
formation of silver hollow
spheres by the two-step route
Nanoscale Res Lett (2008) 3:82–86 83
123

produced in template synthesis [17], the size is smaller.
The shell of dark edges consists of the silver nanopar-
ticles capped Eu(TTA)
3
Á 2H
2
O complex for assembling,
and the pale regions exclude the possibility alone silver
nanoparticles capped Eu(TTA)
3
Á 2H
2
O complex and free
Eu(TTA)
3
Á 2H
2
O complex as shown in Fig. 1b. It also
further clearly shows that uniformity shell structure of
silver hollow spheres is with the shell thickness ranging
from 40 to 100 nm. From the size of isolated silver
nanoparticles (21.5 nm), we can determine that the shell
is formed by 2–5 layers of silver nanoparticles aggre-
gate. Typical electron diffraction pattern image of Ag
nanoparticles is also shown in Fig. 1c, which shows
growing parallel to (111), (200), and (220) planes of
cubic silver, indicating the hollow spheres containing
crystal Ag.
The UV–Vis absorption spectrum of the silver hollow
spheres and pure Eu(TTA)

3
Á 2H
2
O in THF solution are
compared in Fig. 2. As is well-known, the peak at
423.2 nm is the surface plasmon resonant absorption of
silver nanoparticles as shown in curve B of Fig. 2, sug-
gesting that the silver hollow spheres consisted of silver
nanoparticles. The surface plasmon resonant absorption
cannot be observed in previous work [17] because the
silver hollow spheres are submicrometer and do not consist
of silver nanoparticles. At the same time, an observation of
the two curves A and B shows the almost same p–p*
absorption peak (343.9 and 345.7 nm) of TTA, which is
different from previous work [16, 18, 19]. The result is
attributed that the additional free Eu(TTA)
3
Á 2H
2
O do not
form J-aggregate and only acts as bridge between silver
nanoparticles. The result further confirms that the forma-
tion of silver hollow spheres by self-assemble of Ag
nanoparticles assisted with Eu(TTA)
3
Á 2H
2
O.
To further confirm the formation of silver hollow
spheres, the typical surface morphology of SNOM is shown

in Fig. 3. Figure 3a suggests that the silver hollow spheres
are an average diameter of 0.9 lm, which is consistent with
the result of TEM images. The typical transmission image
of SNOM of the silver hollow spheres is further
Fig. 1 (a) TEM images of the
silver hollow spheres, (b)
HRTEM images of the silver
hollow spheres, and (c)ED
pattern of the silver hollow
spheres
84 Nanoscale Res Lett (2008) 3:82–86
123
characterized in Fig. 3b, indicating that the in-laser at
457 nm is almost absorbed for plasmon resonant absorp-
tion of silver nanoparticles. The result further confirms that
the silver hollow spheres shown in Fig. 3a are attributed to
the silver nanoparticles assembling.
The surface properties of silver hollow spheres are
further shown in the SEM images (Fig. 4). It shows that
the spheres are indeed hollow at magnification and sug-
gests that the silver hollow spheres consist entirely of
uniform silver nanoparticles in the diameter of 21.5 nm.
Figure 4b also indicates that the outer surface of these
silver hollow spheres is not perfectly smooth. From SEM
observation the proportion of broken spheres appears to be
\1% (Fig. 4a), the present silver hollow spheres are
much more difficult to break, resulting from that the silver
shells are much more robust compared with the metal
hollow spheres produced previously in other synthesis
routes [20–22].

300 400 500 600
0.0
0.1
0.2
0.3
0.4
B
A
343.2nm
423.2nm
345.7nm
Abs(a.u)
Wavelength(nm)
Fig. 2 (a) The UV absorption of pure Eu(TTA)
3
Á 2H
2
O complexes
and (b) silver hollow spheres in THF solution
Fig. 3 (a) The SNOM surface
image of silver hollow spheres.
(b) The SNOM transmittance
image of silver hollow spheres
Fig. 4 (a) SEM images of the
silver hollow spheres and (b)
HRFSEM images of the silver
hollow spheres
Nanoscale Res Lett (2008) 3:82–86 85
123
The fluorescent properties of silver hollow spheres are

also investigated as shown in Fig. 5, along with pure
Eu(TTA)
3
Á 2H
2
O complexes solution. The left curves
show the similar excitation peak of 342.0 nm for silver
hollow sphere and Eu(TTA)
3
Á 2H
2
O complex solution,
which is consistent with previous work [16]. The emission
spectra of silver hollow sphere and Eu(TTA)
3
Á 2H
2
O
complex solution are shown in right curves of Fig. 5, too.
The similar emission spectra provide the typical red
luminescent peaks at 592.0 and 613.0 nm, which is
attributed to
5
D
0
–
7
F
0–1
transitions of Eu(III) ion, by exci-

tation at 342.0 nm. However, the emission strength of
silver hollow sphere solution is slightly lower than that of
pure Eu(TTA)
3
Á 2H
2
O complexes solution. These fluo-
rescent spectra provide value information about
interactions of silver nanoparticles aggregate to silver
hollow sphere. These results show that the silver hollow
sphere is expected to be a new kind of fluorescent material.
Conclusions
In conclusion, silver hollow spheres have been successfully
synthesized using two-step approach. This radiation syn-
thetic pathway provides an important example of well-
ordered and functional silver hollow spheres with designed
morphology. The unique silver shell structure obtained
here may be promising candidates for both fundamental
research and application, and it is believed that assembling
synthesis based on functional molecules represents a novel
route to prepare functional inorganic hollow sphere, which
is a topic of intense interest. Moreover, the silver hollow
spheres have high luminescent property at 614.3 nm, which
is to be applied in optical materials.
Acknowledgments This work was supported by the National Nat-
ural Science Foundation of China (No: 50025309, and No:
90201016), Youthful Science Foundation of Shanxi province (No:
P20072185 and No: P20072194), and Youthful Science Foundation of
North University. The authors are grateful for the financial support
and express their thanks to Hui Zhao for helpful discussions and Wan

Qun Hu for IR measurements.
References
1. R. Langer, Science 249, 1527 (1990)
2. I. Gill, A. Ballesteros, J. Am. Chem. Soc. 120, 8587 (1998)
3. J. Ding, G. Liu, Macromolecules 31, 6554 (1998)
4. F. Caruso, S.A. Davis, H. Mohwald, Angew. Chem. Int. Ed. Engl.
37, 2202 (1998)
5. K.B. Thurmond, T. Kowalewski, K. Wooley, J. Am. Chem. Soc.
119, 6656 (1997)
6. R. Sampsa, R. Isabel, F.J. Garcı
´
a de Abajo, Phys. Rev. B 71,
235104 (2005)
7. O. Noriyuki, H. Yasushi, N. Arao, S. Isabel Pastoriza, M. Luis,
M. Liz, J. Phys. Chem. B 108, 8751 (2004)
8. D. Zhang, L.M. Qi, M. Jiming, Adv. Mater. 14, 1499 (2002)
9. L.M. Wang, D.J. Chen, Mater. Lett. 61(10), 2113 (2007)
10. S.W. Michael, N.C. Jennifer, C. Kyoung-Shin, J.D. Timothy,
D.S. Galen, Nano Lett. 2, 583 (2002)
11. T. Andrea, K. Franklin, H. Christian, G. Joshua, H. Rongrui,
S. Yugang, X. Younan, Y. Peidong, Nano Lett. 3, 1229 (2003)
12. S. Murali, K.S. Mayya, D.V. Paranjape, S.G. Hegde, J. Phys.
Chem. B 10, 4954 (1997)
13. C. Won San, Y.K. Hye, P. Jeong-Ho, K. Dong-Yu, J. Am. Chem.
Soc. 127, 16136 (2005)
14. S. Youyi, Z. Qijin, et al., Mater. Lett. 60(21–22), 2756 (2006)
15. H.F. Jiu, W. Su, et al., Chin. J. Chem. Phys. 17, 4460 (2004)
16. S. Youyi, J. Hongfang, Z. Douguo, G. Jiangang, G. Bin, Z. Qijin,
Chem. Phys. Lett. 410, 204 (2005)
17. K.L. Sooklal, H. Hanus, H.J. Ploehn, C. Murphy, J. Adv. Mater.

10, 1083 (1998)
18. K.Z. Wang, L.H. Gao, C.H. Huang, J. Photochem. Photobiol. A
156, 39 (2003)
19. G.L. Zhong, Y.H. Wang, C.K. Wang, B.Y. Pu, et al., J. Lumin.
99, 2 (2000)
20. D. Walsh, B. Lebeau, S. Mann, Adv. Mater. 11, 324 (1999)
21. T. Liu, Y. Xie, B. Chu, Langmuir 16, 9015 (2000)
22. L. Qi, J. Li, Adv. Mater. 14, 300 (2002)
Fig. 5 Fluorescent spectra of (a) pure Eu(TTA)
3
Á 2H
2
O complexes
and (b) silver hollow spheres in THF solution
86 Nanoscale Res Lett (2008) 3:82–86
123